1. Field of the Invention
The present invention relates to a toner, a developer including the toner, and an image forming method, an image forming apparatus and a process cartridge using the toner.
2. Discussion of the Background
In image forming apparatus such as electrophotographic image forming apparatus and electrostatic recording apparatus, images are prepared by a method including the following processes:    (1) an electrostatic image is formed on an image bearing member such as photoreceptors and dielectric materials (electrostatic latent image forming process);    (2) the electrostatic image is developed with a developer including a charged toner to prepare a toner image on the image bearing member (developing process);    (3) the toner image is transferred to a receiving material optionally via an intermediate transfer medium (transfer process);    (4) the toner image is heated to fix the toner image on the receiving material (fixing process); and    (5) toner particles remaining on the surface of the image bearing member are removed therefrom such that the image bearing member is ready for the next image forming operation (cleaning process).
The toner for use in such an image forming method includes at least a binder resin and a colorant, and optionally includes a charge controlling agent, a release agent and other additives.
Recently a need exists for an electrophotographic image forming apparatus capable of producing high quality images, particularly, high quality full color images. Full color images produced by electrophotographic copiers are inferior to those produced by printing machines in image quality. Therefore, electrophotographic copiers are required to produce high definition images having as good image quality as those of photographs and prints. In attempting to produce high quality images, various toners have been proposed. In order to produce high quality images, the toner used therefor is required to have the following properties:    (1) a good developability so as to efficiently and faithfully develop an electrostatic latent image;    (2) a good transferability so as to be efficiently transferred to a receiving material;    (3) a good fixability so as to be fixed in a wide fixing temperature range without causing an offset problem; and    (4) a good cleanability so as to be well removed from an image bearing member by a cleaner.
For example, in order to impart good developability, transferability and cleanability of a toner, it is attempted to improve the charge properties of the toner. Specifically, it is described in Japanese Patents Nos. 2,942,588 and 3,102,797 that by using a toner including a specific fluorine-containing ammonium salt as a charge controlling agent, the charge properties of the toner can be improved. However, when such a fluorine-containing ammonium salt is used for a toner, there is a case where the fixability of the toner deteriorates (specifically, the fixable temperature range narrows) although the charge properties of the toner can be improved. In addition, it is described in Japanese Patent No. 3,407,521 that by localizing a fluorine-containing compound on the surface of toner particles while controlling the atomic ratio of fluorine atoms to carbon atoms on the surface of the toner particles, the charge properties of the toner can be improved. However, such a technique has a drawback in that the fixability of the toner deteriorates.
As for the fixability, it is described in published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 11-133667 that by using a polyester resin modified so as to have a urea bonding as a binder resin, the high temperature preservability and low temperature fixability can be improved. However, as a result of the present inventors' study, it is found that by using only such a polyester resin, the charge stability to withstand various environmental conditions is hardly improved (namely, the charge of the toner considerably changes when temperature and humidity changes, for example, from normal temperature and humidity conditions to high (or low) temperature and high (or low) humidity conditions).
In addition, it has been described in JP-As 2003-076056 and 2003-167369 that by controlling the methanol wettability, which will be explained later in detail, of a toner so as to be from 35 to 60% by volume, the stability to withstand various environmental conditions and the charge quantity distribution of the toner can be improved. However, as a result of the present inventors' study, it is found that only by controlling the methanol wettability, good stability to withstand environmental conditions of the toner cannot be controlled. In this regard, good stability to withstand various environmental conditions means a good combination of charge and preservation stabilities to withstand various environmental conditions, and is hereinafter referred to as environmental stability. Namely, a toner having good environmental stability is such that even when the toner is preserved under high (or low) temperature and high (or low) humidity conditions, the toner can maintain good chargeability, transferability, fixability and cleanability while the toner particles hardly cause agglomeration.
Further, it is described in JP-A 2003-050477 that by controlling the tensile strength of a toner so as to be from 10 to 1400 N/m2 when the toner is pressed at a pressure of 10 kg/cm2, a good combination of developability and transferability can be imparted to the toner. However, as a result of the present inventors' study, it is found that only by controlling the tensile strength, there is a case where the developability and transferability of the toner cannot be fully improved.
Because of these reasons, a need exists for a toner having a good combination of developability, transferability, fixability, cleanability and environmental stability.